It is proposed to investigate in the young adult rabbit the functional and structural features of resistance vessels of 70-200 microns o.d. Characteristics related to the adrenergic control of these vessels from the pial, mesenteric, lower limb and ear vascular beds will be emphasized. This study of vessels from healthy animals will preface a longitudinal time-course investigation of the alteration of these features in two rabbit models of experimental hypertension: the rabbit with partial abdominal aortic constriction and that with sinoaortic denervation. A parallel study will be made of mesenteric resistance vessels from age and sex matched young human normotensive and hypertensive subjects. Parameters to be studied are those which will assess (a) adrenergic nerve terminal function - pattern of innervation, varicosity density, norepinephrine content and release, (b) adrenergic synaptic transmission - intrasynaptic transmitter concentration, neuromuscular relationships, transmitter action and disposition and (c) structure and function of the vascular wall - wall dimensions, elasticity, smooth muscle cell number, size and proliferation, spontaneous contractility and tone and alpha and beta-adrenoceptor mediated responses. A longitudinal study of changes in resistance vessels and their adrenergic regulation these two hypertensive models will indicate what changes in vascular structure and function are initiated by an increase in sympathetic activity during development and at maturity. This may be relevant to the class of primary hypertensive patients in which changes in sympathetic activity occurs. Thus, this combined approach will help in interpretation of t significance and basis of changes in vessels from animals and patients with hypertension measured by similar techniques in the same laboratory.